Robert Fripp - Cirkus (King Crimson). A twisted, acoustic rampage.
Robert Fripp - Fracture (King Crimson). All of it. Just all of it.
Jonny Greenwood - Paranoid Android (Radiohead). Not my favourite RH solo but definitely one of the most defining.
Jonny Greenwood - Go To Sleep (Radiohead). Specifically the Glastonbury live version with full Max/MSP power.
Tom Morello - Bulls on Parade (Rage Against the Machine). Redefines what a 'solo' is.